The present invention relates to a method for measuring the tread of a tire, especially a pneumatic vehicle tire, whereby the measurement of the tread depth is effected in the operating state while the tire is rolling and in contact with a surface below it. The present invention also relates to a tire for carrying out such a method as well as the use thereof.
Methods for detecting the tread depth of a tire in the operating state, i.e. while the tire is rolling and in contact with the ground, in other words while the vehicle is moving, are known in principle and serve for generating a warning for the driver or monitoring personnel as early as possible before a lower limit that is critical for the tread depth is reached.
DE PS 596 861 discloses, for example, an indicator apparatus for the maximum permissible wear of rubber tires, according to which spring elements are disposed in the tread of the tire that after a certain thickness of the rubber layer has been worn away spring outwardly and trigger alarm signals electrically as the tire rotates. The drawback of such spring elements include an increased weight of the tire and a more difficult manufacturing process for such tires.
DE OS 2 314 915 discloses a vehicle tire in which one or more differently colored or structured layers are embedded in the tread or profiled surfaces, with such layers differing from the remaining wear surfaces that are provided and becoming visible after a certain amount of wear of the tread. However, the visibility of such layers is very adversely affected during operation due to dirt or deposits.
It is therefore an object of the present invention to provide a method for the detection of the tread or profile depth of a tire in the operating state, with such method being easy to use, and not only with heavier tires or with a more complicated manufacturing process, and which is capable of functioning in all operating states and even in dirty environments.
The method of the present invention is characterized primarily in that the vibrations of the tire or of parts thereof, which vibrations are generated by the spacing and/or geometry of the profiled elements of the tire tread while the tire is rolling and in contact with the surface below it, are detected and are compared, in an evaluation unit, with a characteristic theoretical value/threshold value for the vibrations, which characteristic value corresponds to a vibration generated by a tread of adequate depth, whereby the evaluation unit issues a signal if a detected vibration deviates from the theoretical value/threshold value, which deviation corresponds to a tread depth that is less than the adequate depth.
In this way, it is possible at any time to check the tread depth by means of an actual vibration evaluation that can be carried out relatively economically and without complicated devices with the aid of today""s electronics and the processing of even complex algorithms that are possible therewith; this checking of the tread depth can in particular be realized in that the output signal, namely the vibrations, in other words for example the operating noises of a tire, produced by the spacing and/or geometry of the profiled elements of the tire tread, is permanently present and does not first have to be generated.
Pursuant to one advantageous specific embodiment of the present invention, it is the body vibrations/structure-borne noise vibrations of the tire or of the chassis or body parts, and which are generated by the spacing and/or geometry of the profiled elements of the tire tread, that are detected. To receive the vibrations, a simple vibration sensor on the body or chassis components suffices, which can be mounted, for example, in the vicinity of the tire.
Pursuant to a further advantageous embodiment of the present invention, it is the noises/air-borne noise vibrations of the tire or of the chassis or body parts, which are generated by the spacing and/or geometry of the profiled elements of the tire tread, that are detected. To receive the vibrations, a simple microphone suffices, which can be mounted, for example, in the vicinity of the tire.
With a tire that is particularly suitable for carrying out such a method, as the tread depth decreases the spacing and/or geometry of the profiled elements of the tire tread vary such that while the tire is rolling and in contact with a surface below it, a vibration is generated that is characteristic for the decreased tread depth and that is clearly distinguishable from a characteristic vibration generated by the full tread depth. This simplifies the defined detection and hence the specific determination of the critical tread depth.
Pursuant to one advantageous specific embodiment of such a tire, the geometry of the profiled elements of the tire tread is such that the positive portion of the profiled elements increases or decreases as a function of the tread depth. In this way there is obtained a vibration frequency that is altered at a reduced tread depth.
Pursuant to a further advantageous specific embodiment of such a tire, the spacing of the profiled elements of the tire tread is such that there results a pitch sequence that is a function of the tread depth. Here also there consequently results a vibration frequency that is altered at a reduced tread depth. This effect is reinforced even further in that the spacing of the profiled elements of the tire tread varies in an essentially sudden manner as the tread depth decreases essentially due to the fact that tread depths of lesser height are provided that come into contact with the surface of the roadway only after a wear of the adjacent tire tread depths, and then make contact relatively suddenly.